1. Field of the Invention
The present invention relates to a magnetoresistive element and a method of manufacturing the same, e.g., a magnetoresistive element capable of recording information by supplying a current in two directions, and a method of manufacturing the same.
2. Description of the Related Art
A magnetic random access memory (MRAM) using a ferromagnetic material is expected as a nonvolatile memory that achieves high-speed operation, large capacity, and low power consumption. The MRAM includes a magnetic tunnel junction (MTJ) element using the tunneling magnetoresistive (TMR) effect as a memory element, and stores information in accordance with the magnetization configuration of this MTJ element.
In the conventional MRAM in which data is written by a magnetic field generated by a line current, the coercive force increases as the size of the MTJ element decreases. This often increases a current necessary for data write. In this conventional MRAM, it is difficult to achieve a small cell size for obtaining large capacity and low current at the same time.
A spin-injection-type MRAM using the spin momentum transfer (SMT) write method as a write method that solves the above problem has been proposed. In this spin-injection-type MRAM, information is written by directly supplying a current to the MTJ element, and changing the magnetization direction in a free layer in accordance with the direction of the current. Also, an MTJ element comprising two fixed layers sandwiching a free layer can increase the spin torque. This makes it possible to reduce the critical current density of the MTJ element.
When forming an MTJ element like this, a double magnetic tunnel junction is separated into MTJ elements in an etching step. However, the reaction product formed by etching during junction separation adheres to the side surfaces of the element, and short circuits the free layer and fixed layer. To avoid this short circuit of the free layer and fixed layer, taper etching can be performed. However, the processed sectional shape becomes a tapered shape, and the increase in etching film thickness caused by the two fixed layers increases the processing conversion difference during taper etching. This increases the MTJ element size.
As a related technique of this kind, a technique that improves the characteristics and reliability of an element by preventing the generation of, e.g., a metallic polymer when forming an MTJ cell is disclosed (Jpn. Pat. Appln. KOKAI Publication No. 2004-214600).